1. Field of the Invention
The present invention relates to a high-frequency receiving unit and a high-frequency receiving method suitably used for a portable broadcast receiving terminal or the like for receiving especially satellite digital broadcast.
2. Description of the Related Art
As is well known, at the present, a satellite digital broadcast system using a frequency band of 2.6 GHz has been developed. The main service target of this satellite digital broadcast system is mobile units such as a portable broadcast receiving terminal.
Further, this satellite digital broadcast system is not only positioned as digital audio broadcast of high audio quality but also is greatly expected as broadcast media capable of delivering multimedia contents including simple moving pictures to the mobile units.
Other novel media include a terrestrial digital broadcast system designed for fixed receivers, but this system limits the region where the receivers can receive the broadcast and is predicated on the receivers being used near a transmitting antenna. However, in the above satellite digital broadcast system, broadcast radio waves can be received in any places where the broadcast radio waves from a geostationary satellite arrive.
The portable broadcast receiving terminals under the present state commonly use rod antennas as antennas but terminals mounted with helical antennas have also come on the market.
However, in these structures, the antenna is protruded outside from the main body of the broadcast receiving terminal and hence is inconvenient for carrying the terminal, which creates a need to improve the antenna in terms of user's handling.
Further, in order to cope with this problem, it is thought that a chip antenna is used as the antenna. By adopting this chip antenna, the antenna itself is not protruded outside from the main body of the broadcast receiving terminal.
However, when the chip antenna is packaged, the circuit pattern and its peripheral earth pattern of a printed circuit board need to be removed. There is presented a problem that the chip antenna expands a substantial footprint wide to impair reducing the physical size of the chip.
Still further, the user operates the portable broadcast receiving terminal and watches or listens to broadcast contents with the terminal in his hand. For this reason, at the time of putting the satellite digital broadcast system into practical use, it is necessary to take measures to make the broadcast receiving terminal effectively receive broadcast radio waves from the satellite without interference.
In particular, in the satellite digital broadcast system, there are cases where broadcast contents are only audio, so it is envisaged that the user receives the broadcast contents with the terminal in the pocket of user's clothes without watching a display screen.
In this case, since the position of the broadcast receiving terminal in vertical and horizontal directions is not determined, the broadcast receiving terminal needs to satisfy as wide directivity as possible so that it can receive broadcast under good conditions even if it is placed in any direction.
Here, in Jpn. Pat. Appln. KOKAI Publication No. 10-308941 is disclosed a satellite broadcast system which can be received by a simple receiver responding to needs not only for indoor use but also for mobile unit or portable unit. However, in this Jpn. Pat. Appln. KOKAI Publication No. 10-308941 is disclosed a configuration of improving the transmitting antenna itself of the satellite and hence is not suitable for commercialization.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 8-23482 is disclosed an antenna control device which is applied to a television set used in a mobile state such as a liquid crystal television set and the like and can receive pictures and audios under stable good conditions.
However, in this Jpn. Pat. Appln. KOKAI Publication No. 8-23482, signals received by two receiving antennas are added and the gain of the signal received by one receiving antenna is controlled on the basis of the added signal level. Hence, a circuit construction increases in complexity and hence is not suitable for commercialization.
Further, in Jpn. Pat. Appln. KOKAI Publication Nos. 10-262199 and 10-313208 is disclosed a configuration in which a plurality of antennas are packaged in the case of a portable receiving unit. However, in these Jpn. Pat. Appln. KOKAI Publication Nos. 10-262199 and 10-313208, there is disclosed a configuration that the plurality of antennas are connected in series to obtain a plurality of resonant frequencies to thereby expand a reception frequency band but there is no reference made to improving directivity characteristics for the purpose of receiving broadcast by a portable broadcast receiving terminal.
Still further, in Jpn. Pat. Appln. KOKAI Publication No. 2002-151928 is disclosed a construction in which an antenna element is arranged away from a metal element to improve directivity as a receiving unit. However, in this Jpn. Pat. Appln. KOKAI Publication No. 2002-151928, because a chip antenna is used, the footprint of an earth pattern needs to be expanded. For this reason, the chip antenna can be packaged in a portable unit having as large a size as a notebook type personal computer, for example, but it becomes difficult to put the chip antenna into practical use for a potable unit smaller than this.